The Collaborative International Dictionary of English v.0.48:

Ectoparasite \Ec`to*par"a*site\, n. (Zo["o]l.)
   Any parasite which lives on the exterior of animals; --
   opposed to endoparasite. -- Ec`to*par`a*sit"ic, a.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ectoparasite
    n 1: any external parasitic organism (as fleas) [syn:
         ectoparasite, ectozoan, ectozoon, epizoan,
         epizoon]